Question 1

Which of the following best explains why lipids are largely insoluble in water?

Accepted Answer

They contain long hydrocarbon chains that are nonpolar, making them hydrophobic.

Question 2

A scientist adds phospholipids to water and observes the formation of spherical structures with hydrophobic tails facing inward. What are these structures called, and why do they form?

Accepted Answer

Micelles; they form because the hydrophobic tails avoid water while the hydrophilic heads interact with water.

Question 3

Which of the following statements about cholesterol in animal cell membranes is correct?

Accepted Answer

Cholesterol decreases membrane permeability by filling spaces between phospholipids.

Question 4

A phospholipid is described as amphipathic. What does this mean?

Accepted Answer

It has both hydrophilic and hydrophobic regions.

Question 5

Which of the following best describes the structure of a fat (triglyceride)?

Accepted Answer

Three fatty acids linked to a glycerol molecule by ester linkages.

Question 6

If a cell membrane is composed primarily of phospholipids with long, saturated hydrocarbon tails, what effect does this have on membrane permeability?

Accepted Answer

It decreases membrane permeability because the tails pack tightly together.

Question 7

Which of the following molecules would most easily cross a pure phospholipid bilayer?

Accepted Answer

Oxygen ($O_2$)

Question 8

A researcher increases the temperature of a cell membrane. What is the most likely effect on membrane fluidity and permeability?

Accepted Answer

Both fluidity and permeability increase as temperature rises.

Question 9

Which of the following best explains why unsaturated fatty acids increase membrane fluidity?

Accepted Answer

The double bonds create kinks, preventing tight packing of the tails.

Question 10

A patient has a genetic disorder that prevents the synthesis of cholesterol. Which of the following is a likely consequence for their cell membranes?

Accepted Answer

Their membranes will be more permeable and less stable, especially at high temperatures.

Question 11

Which of the following is NOT a function of the plasma membrane?

Accepted Answer

Synthesizing proteins for the cell.

Question 12

Which of the following best describes selective permeability in biological membranes?

Accepted Answer

Some substances cross the membrane more easily than others.

Question 13

Which of the following statements about phospholipid bilayers is correct?

Accepted Answer

They form spontaneously in water due to the amphipathic nature of phospholipids.

Question 14

A cell membrane is experimentally altered to contain more unsaturated fatty acids. What is the most likely effect on the cell?

Accepted Answer

The membrane will become more fluid and more permeable.

Question 15

Which of the following best explains why oil and gasoline do NOT form micelles or liposomes in water?

Accepted Answer

They are not amphipathic and lack a hydrophilic region.

Question 16

Which of the following is a correct statement about the permeability of a phospholipid bilayer?

Accepted Answer

Small, nonpolar molecules cross quickly, while large or charged molecules cross slowly, if at all.

Question 17

A biologist creates a liposome with 10% cholesterol. Compared to a liposome with 0% cholesterol, what would you expect?

Accepted Answer

The membrane will be less permeable with 10% cholesterol.

Question 18

Which of the following is a correct description of a fatty acid?

Accepted Answer

A hydrocarbon chain bonded to a carboxyl ($-COOH$) group.

Question 19

Which of the following would DECREASE the fluidity of a cell membrane at room temperature?

Accepted Answer

Increasing the proportion of saturated fatty acids.

Question 20

A cell is exposed to a cold environment. Which of the following changes would help maintain membrane fluidity?

Accepted Answer

Increasing the proportion of unsaturated fatty acids in the membrane.

Lipids and Membrane Structure: Study Notes for BIOL 111

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